Electric induction heating apparatus



Dec. 3, 1940. N. R. STANSEL ELECTRIC INDUCTION HEATING APPARATUS Filed April 29, 1939 Inventor": Numan 1Q. Stans'el His Attorney.

Patented 3, 1940 UNITED STATES PATENT ornca ELECTRIC INDUCTION HEATING APPARATUS Numan n. Stansel, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application April 29, 1939, Serial No. 270,818

2 Claims. I (Cl. 21913) My invention relates to electric induction heat acterized by the fact that the generation of heat is confined to a thin outer layer which maybe 15 heated to a hardening temperature without heating the interior of the article to that temperature. However, this method heats the entire surface of the article whereas in some articles, such as steel rails for railroads, it is desirable to heat the go top wearing surface only.-

In accordance? with my invention, I provide a shield for the body to be heated which shield is made of high electrical conductivity material, preferably copper, and is arranged to surround 25 the body except for the portion or surface of the body which is to be heated. This shield is of such thickness as to substantially prevent interlinkage of the high frequency magnetic flux with all portions of the body covered by it.

30 For a more complete understanding of my invention, referenceshould be had to the accompanying drawing in which Fig. 1 is an elevation view of a high frequency induction heater for railroad rails embodying my invention, while Fig.

35 2 is an enlarged view in section taken along the line 2-2 of Fig. 1 looking in the directionof the arrows.

Referring tothe drawing, I have-shown my-in-- vention in one form'as applied to the-heating of o the treads on the ends of railway rails for the purpose of hardening the treads. This hardening is desirable t prevent the excessive wear at the ends of the rails occasioned by the joint between the rails.

5 The heating apparatus comprises a helical high frequency heating or magnetic flux inducing primary winding which is large enough to provide for the insertion of the ends of two rails ll and I! in aligned and abutting relation in the 50 winding as shown in Fig. 1. The rails and the heating winding are mounted on suitablesupthe top being in closely spaced relation with the top or tread portion I! of the rail which is to be heated. The conductor of the winding I0 is made from a tube in the conventional manner so that cooling water may be circulated through it. It is 5 supplied bymeans of conductors l6 and il with a current of suitable high frequency, preferably 7 on the order of two thousand cycles.

Unless some means were provided to prevent it, the entire surfaces of the rails at their two 19 ends inserted in the winding would be heated; It is desired however to heat only the tread, i. e., the top portion ll at'the ends of the two rails. For the purpose of shielding the remaining surfaces of the rails from interlinkage by the electromagnetic flux set up by the winding In, I have provided a shield l9 which surrounds the rails except for the tread surface I! and thereby prevents the generation of heat in all portions except the treads. This shield is preferably. made of a 20 material having a good'electrical conductivity, such as copper. As shown, it loosely conforms with the shape of the rails and is provided with g a top opening 20, exposing the tread l8, and strengthening .ribs 2|. lit-extends between the supports l3 and I4 and is supported at each end on the supports. It will be noted that the shield because of the top opening 20 is discontinuous sheet metal having a uniform thickness, which thickness in a direction-radial with respect to the coil l0 would in practice be about V4 inch with a frequency of approximately two thousand cycles. For the most effective shielding the thickness must be not less than three times the equivalent 40 depth of penetration of uniform magnetization as expressed by Steinmetz (Theory and Calculation of Transient Electrical. Phenomena and Oscillations, 3rd edition, 1920, p.371) as follows:

wherein p equals equivalent depth of penetration,

in centimeters, p equals resistivity of the material of the shield in ohms cm., I equals frequency, cycles per second. a equals permeability of the metal of the shield equals 1'! opper.

A shield having a thickness eq al tofour times the equivalent depth of penetration as given by the above formula, absorbs about 98 per cent of so shield made of copper inside said winding ar-- It will be understood that the apparatus will be designed to heat the tread surface l8 quickly to a desired hardening temperature of 900 C; or

higher after the insertion of the rails or the application of power to the winding in, perhaps in a period of a few seconds; This quick heating is required to effect the heating of a surface layer at the tread, such as A; to I; of an inch in thickness, to the hardening temperature so quickly that the inner portion of the rail is not appreciably heated by conduction of heat from the surface. The rails are then removed and quenched immediately.

' The frequency used is selected as a compromise between the thickness ofthe shield, the exciting current, the voltage of" the supply source, and

cost of the apparatus, there being considerable leeway in connection with the required heating effect.

While I have shown a particular embodiment of my invention, it will be understood, of course, that I do not wish to be limited thereto, since many modifications may be made and I, therefore, contemplate bythe appended claims'to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. Apparatus for heating a predetermined surface-portion to a predetermined depth of a body made of magnetic material, comprising a primary induction heating winding of such size that the body to be heated may be inserted therein so as I to be surrounded by said winding, a magnetic ranged to surround the body except for said surface portion to be-heated, said shield being dis-' continuous electrically in a circumferential direction throughout substantially its entire length and projecting from each end of said windingso as to exclude substantially the magneticflux produced by said winding from the surface of the body inserted in said winding except said predetermined surface; and electric connections for supplying high frequency current to said winding whereby a magnetic flux is caused to interlink with saidsurface portion and thereby heat said surface portion to a. predetermined temperature, said shield having a thickness in a direction radial of said winding sumcient to exclude substantially all magnetic flux set up by said winding from all other surface portions of the body.

2. A high frequency induction heating apparatus for heating the treads oi steel rails and the like to hardening temperatures, comprising a primary induction heating winding of such size that the rail to be heated may be inserted loosely therein so'as to be surrounded by said winding and with the tread to be heated closely adjacent the turns of said winding, a magnetic shield made of copper inside said, winding arranged to surround the rail except for the tread to be heated, said shield having substantially the cross sectional shape of the rail to be heated and being discontinuous electrically in a circumferential direction but structurally continuous axially throughout substantially its entire length and projecting from each end of said winding so as to excludesubstantially the magnetic flux produced by said winding from the surface of the rail inserted in said winding except the tread to be heated, and electric connections for supplying a high frequency current to said winding whereby a magnetic flux is caused to Interlink with the tread and thereby heat the tread to a predetermined temperature, said shield having a ,thickness in a direction radial of said winding sufli cient to exclude substantially all magnetic flux set up by said winding from all other surface portions of the rail enclosed by said winding.

'NUMAN R. STANSEL. 

